However, atorvastatin, with the brand name Lipitor, did not have any effect.

The study, published in PLOS ONE, found adverse effects of pravastatin on memory could be reversed by stopping the medication.

Neil Marrion, professor of neuroscience at Bristol's School of Physiology and Pharmacology and the study's lead author, said: ''This finding is novel and likely reflects both the anecdotal reports and FDA advice.

''What is most interesting is that it is not a feature of all statins.

''However, in order to better understand the relationship between statin treatment and cognitive function, further studies are needed.''

The research examined adverse effects on memory from prescribed statin medicines, used to lower low-density lipoprotein (LDL) in the blood.

Results showed rat performance for simple learning and memory tasks were impaired when taking pravastatin, but not atorvastatin.

The rats were treated daily with pravastatin or atorvastatin for 18 days.

The rodents were tested in a simple learning task before, during and after treatment, in which they had to learn where to find a food reward.

The rats also performed a task which measured their ability to recognise a previously encountered object, on the last day of treatment and a week after it finished.

Pravastatin tended to impair learning over the last few days of treatment, though this was fully reversed once the rats stopped taking the medicine.

In the novel object discrimination task, object recognition memory was also impaired by pravastatin.